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Microorganisms : The Cause of Diseases in Human Beings | Immunology

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Microorganisms : The Cause of Diseases in Human Beings!

Centuries back man has realized that diseases like cholera and typhoid spread very fast in densely populated areas and he isolated and kept the diseased individuals in separate places with the idea that the spread of disease from patients to normal individuals could be prevented.

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The concept that there may be some small unseen organisms responsible for diseases is very old. For centuries scientific evidence was not available to support this concept. In 1674, Anton van Leeuwenhoek improved the art of polishing lenses of short focal length.

He discovered and described protozoa, bacteria, rotifers, and the like. In 1677 Anton van Leeuwenhoek described human spermatozoa and asserted that they were capable of developing into a child. With the help of the microscope, which Anton van Leeuwenhoek invented, it became possible to describe organisms not visible to be naked eye. Innovation of microscope was an important landmark in the development of microbiology and immunology.

Louis Pasteur and Robert Koch were instrumental in defining microorganisms as the etiological agents of many diseases. As said earlier, the concept that small germs are responsible for many diseases was evolving over a period of many centuries. With the invention of microscope, microbiology advanced very fast. In 1850, Casimir Davaine reported that he could see anthrax bacilli in the blood of infected sheep.

Louis Pasteur was born in France. He was a chemist and worked on several topics. Louis Pasteur, who was interested in the fermentation of beer, wine and meat decay, was the first to isolate microorganisms from ferments. He discovered that alcohol fermentation was caused by living organisms and that bacteria were responsible for producing lactic acid in wine.

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In 1864, Louis Pasteur disapproved the theory of spon­taneous generation. He proposed the ‘Germ theory of disease’, which suggests that most diseases are caused by microorganisms, transmitted from an infected individual to a non-infected individual. He purified the microorganisms and introduced them to fresh materials (like beer, wine, and meat) and demonstrated the transfer of fermentation by microorganisms. He also demonstrated that this transfer could be stopped by heating (pasteurization). He developed attenuated vaccines against anthrax, chicken cholera, and rabies.

In the 1850s the silk industry in France was seriously affected by a disease of silkworms. Pasteur demonstrated the presence of a microbe in the diseased silk worms. He also demonstrated that the transfer of the microbe from the affected silkworms to the unaffected silkworms transferred the condition to the unaffected silkworms.

Robert Koch, a German scientist was the first to isolate the anthrax microbe, though it was Pasteur who demonstrated the ability of the anthrax microbe to transfer disease. Anthrax bacillus was first transmitted from in vitro culture to animals by Robert Koch in 1876.

Robert Koch worked extensively on tuberculosis. Koch was the first to isolate the microbe that causes human tuberculosis (1882). He noticed that the inoculation of tubercle bacilli in animal lead to the necrosis of tissues at the inoculated site. The ‘Koch Phenomenon’ later became to be known as delayed type hypersensitivity.

Koch also outlined the parameters required for the identification of an etiologic agent as the cause of a particular disease, which is widely known as ‘Koch’s postulates’. Koch’s postulates are valid even today. At this point of time, many microorganisms responsible for various infectious diseases were discovered. Diphtheria bacillus was discovered by Theodor Klebs and Friederich Loffler in 1883. The concept of aseptic surgery was introduced by Joseph Lister in 1867.